compiler/rustc_feature/src/builtin_attrs.rs

   1 //! Built-in attributes and `cfg` flag gating.
   2
   3 use AttributeDuplicates::*;
   4 use AttributeGate::*;
   5 use AttributeType::*;
   6
   7 use crate::{Features, Stability};
   8
   9 use rustc_data_structures::fx::FxHashMap;
  10 use rustc_span::symbol::{sym, Symbol};
  11
  12 use std::lazy::SyncLazy;
  13
  14 type GateFn = fn(&Features) -> bool;
  15
  16 macro_rules! cfg_fn {
  17     ($field: ident) => {
  18         (|features| features.$field) as GateFn
  19     };
  20 }
  21
  22 pub type GatedCfg = (Symbol, Symbol, GateFn);
  23
  24 /// `cfg(...)`'s that are feature gated.
  25 const GATED_CFGS: &[GatedCfg] = &[
  26     // (name in cfg, feature, function to check if the feature is enabled)
  27     (sym::target_abi, sym::cfg_target_abi, cfg_fn!(cfg_target_abi)),
  28     (sym::target_thread_local, sym::cfg_target_thread_local, cfg_fn!(cfg_target_thread_local)),
  29     (
  30         sym::target_has_atomic_equal_alignment,
  31         sym::cfg_target_has_atomic_equal_alignment,
  32         cfg_fn!(cfg_target_has_atomic_equal_alignment),
  33     ),
  34     (sym::target_has_atomic_load_store, sym::cfg_target_has_atomic, cfg_fn!(cfg_target_has_atomic)),
  35     (sym::sanitize, sym::cfg_sanitize, cfg_fn!(cfg_sanitize)),
  36     (sym::version, sym::cfg_version, cfg_fn!(cfg_version)),
  37 ];
  38
  39 /// Find a gated cfg determined by the `pred`icate which is given the cfg's name.
  40 pub fn find_gated_cfg(pred: impl Fn(Symbol) -> bool) -> Option<&'static GatedCfg> {
  41     GATED_CFGS.iter().find(|(cfg_sym, ..)| pred(*cfg_sym))
  42 }
  43
  44 // If you change this, please modify `src/doc/unstable-book` as well. You must
  45 // move that documentation into the relevant place in the other docs, and
  46 // remove the chapter on the flag.
  47
  48 #[derive(Copy, Clone, PartialEq, Debug)]
  49 pub enum AttributeType {
  50     /// Normal, builtin attribute that is consumed
  51     /// by the compiler before the unused_attribute check
  52     Normal,
  53
  54     /// Builtin attribute that is only allowed at the crate level
  55     CrateLevel,
  56 }
  57
  58 #[derive(Clone, Copy)]
  59 pub enum AttributeGate {
  60     /// Is gated by a given feature gate, reason
  61     /// and function to check if enabled
  62     Gated(Stability, Symbol, &'static str, fn(&Features) -> bool),
  63
  64     /// Ungated attribute, can be used on all release channels
  65     Ungated,
  66 }
  67
  68 // fn() is not Debug
  69 impl std::fmt::Debug for AttributeGate {
  70     fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
  71         match *self {
  72             Self::Gated(ref stab, name, expl, _) => {
  73                 write!(fmt, "Gated({:?}, {}, {})", stab, name, expl)
  74             }
  75             Self::Ungated => write!(fmt, "Ungated"),
  76         }
  77     }
  78 }
  79
  80 impl AttributeGate {
  81     fn is_deprecated(&self) -> bool {
  82         matches!(*self, Self::Gated(Stability::Deprecated(_, _), ..))
  83     }
  84 }
  85
  86 /// A template that the attribute input must match.
  87 /// Only top-level shape (`#[attr]` vs `#[attr(...)]` vs `#[attr = ...]`) is considered now.
  88 #[derive(Clone, Copy, Default)]
  89 pub struct AttributeTemplate {
  90     /// If `true`, the attribute is allowed to be a bare word like `#[test]`.
  91     pub word: bool,
  92     /// If `Some`, the attribute is allowed to take a list of items like `#[allow(..)]`.
  93     pub list: Option<&'static str>,
  94     /// If `Some`, the attribute is allowed to be a name/value pair where the
  95     /// value is a string, like `#[must_use = "reason"]`.
  96     pub name_value_str: Option<&'static str>,
  97 }
  98
  99 /// How to handle multiple duplicate attributes on the same item.
 100 #[derive(Clone, Copy, Default)]
 101 pub enum AttributeDuplicates {
 102     /// Duplicates of this attribute are allowed.
 103     ///
 104     /// This should only be used with attributes where duplicates have semantic
 105     /// meaning, or some kind of "additive" behavior. For example, `#[warn(..)]`
 106     /// can be specified multiple times, and it combines all the entries. Or use
 107     /// this if there is validation done elsewhere.
 108     #[default]
 109     DuplicatesOk,
 110     /// Duplicates after the first attribute will be an unused_attribute warning.
 111     ///
 112     /// This is usually used for "word" attributes, where they are used as a
 113     /// boolean marker, like `#[used]`. It is not necessarily wrong that there
 114     /// are duplicates, but the others should probably be removed.
 115     WarnFollowing,
 116     /// Same as `WarnFollowing`, but only issues warnings for word-style attributes.
 117     ///
 118     /// This is only for special cases, for example multiple `#[macro_use]` can
 119     /// be warned, but multiple `#[macro_use(...)]` should not because the list
 120     /// form has different meaning from the word form.
 121     WarnFollowingWordOnly,
 122     /// Duplicates after the first attribute will be an error.
 123     ///
 124     /// This should be used where duplicates would be ignored, but carry extra
 125     /// meaning that could cause confusion. For example, `#[stable(since="1.0")]
 126     /// #[stable(since="2.0")]`, which version should be used for `stable`?
 127     ErrorFollowing,
 128     /// Duplicates preceding the last instance of the attribute will be an error.
 129     ///
 130     /// This is the same as `ErrorFollowing`, except the last attribute is the
 131     /// one that is "used". This is typically used in cases like codegen
 132     /// attributes which usually only honor the last attribute.
 133     ErrorPreceding,
 134     /// Duplicates after the first attribute will be an unused_attribute warning
 135     /// with a note that this will be an error in the future.
 136     ///
 137     /// This should be used for attributes that should be `ErrorFollowing`, but
 138     /// because older versions of rustc silently accepted (and ignored) the
 139     /// attributes, this is used to transition.
 140     FutureWarnFollowing,
 141     /// Duplicates preceding the last instance of the attribute will be a
 142     /// warning, with a note that this will be an error in the future.
 143     ///
 144     /// This is the same as `FutureWarnFollowing`, except the last attribute is
 145     /// the one that is "used". Ideally these can eventually migrate to
 146     /// `ErrorPreceding`.
 147     FutureWarnPreceding,
 148 }
 149
 150 /// A conveniece macro to deal with `$($expr)?`.
 151 macro_rules! or_default {
 152     ($default:expr,) => {
 153         $default
 154     };
 155     ($default:expr, $next:expr) => {
 156         $next
 157     };
 158 }
 159
 160 /// A convenience macro for constructing attribute templates.
 161 /// E.g., `template!(Word, List: "description")` means that the attribute
 162 /// supports forms `#[attr]` and `#[attr(description)]`.
 163 macro_rules! template {
 164     (Word) => { template!(@ true, None, None) };
 165     (List: $descr: expr) => { template!(@ false, Some($descr), None) };
 166     (NameValueStr: $descr: expr) => { template!(@ false, None, Some($descr)) };
 167     (Word, List: $descr: expr) => { template!(@ true, Some($descr), None) };
 168     (Word, NameValueStr: $descr: expr) => { template!(@ true, None, Some($descr)) };
 169     (List: $descr1: expr, NameValueStr: $descr2: expr) => {
 170         template!(@ false, Some($descr1), Some($descr2))
 171     };
 172     (Word, List: $descr1: expr, NameValueStr: $descr2: expr) => {
 173         template!(@ true, Some($descr1), Some($descr2))
 174     };
 175     (@ $word: expr, $list: expr, $name_value_str: expr) => { AttributeTemplate {
 176         word: $word, list: $list, name_value_str: $name_value_str
 177     } };
 178 }
 179
 180 macro_rules! ungated {
 181     ($attr:ident, $typ:expr, $tpl:expr, $duplicates:expr $(, @only_local: $only_local:expr)? $(,)?) => {
 182         BuiltinAttribute {
 183             name: sym::$attr,
 184             only_local: or_default!(false, $($only_local)?),
 185             type_: $typ,
 186             template: $tpl,
 187             gate: Ungated,
 188             duplicates: $duplicates,
 189         }
 190     };
 191 }
 192
 193 macro_rules! gated {
 194     ($attr:ident, $typ:expr, $tpl:expr, $duplicates:expr $(, @only_local: $only_local:expr)?, $gate:ident, $msg:expr $(,)?) => {
 195         BuiltinAttribute {
 196             name: sym::$attr,
 197             only_local: or_default!(false, $($only_local)?),
 198             type_: $typ,
 199             template: $tpl,
 200             duplicates: $duplicates,
 201             gate: Gated(Stability::Unstable, sym::$gate, $msg, cfg_fn!($gate)),
 202         }
 203     };
 204     ($attr:ident, $typ:expr, $tpl:expr, $duplicates:expr $(, @only_local: $only_local:expr)?, $msg:expr $(,)?) => {
 205         BuiltinAttribute {
 206             name: sym::$attr,
 207             only_local: or_default!(false, $($only_local)?),
 208             type_: $typ,
 209             template: $tpl,
 210             duplicates: $duplicates,
 211             gate: Gated(Stability::Unstable, sym::$attr, $msg, cfg_fn!($attr)),
 212         }
 213     };
 214 }
 215
 216 macro_rules! rustc_attr {
 217     (TEST, $attr:ident, $typ:expr, $tpl:expr, $duplicate:expr $(, @only_local: $only_local:expr)? $(,)?) => {
 218         rustc_attr!(
 219             $attr,
 220             $typ,
 221             $tpl,
 222             $duplicate,
 223             $(@only_local: $only_local,)?
 224             concat!(
 225                 "the `#[",
 226                 stringify!($attr),
 227                 "]` attribute is just used for rustc unit tests \
 228                 and will never be stable",
 229             ),
 230         )
 231     };
 232     ($attr:ident, $typ:expr, $tpl:expr, $duplicates:expr $(, @only_local: $only_local:expr)?, $msg:expr $(,)?) => {
 233         BuiltinAttribute {
 234             name: sym::$attr,
 235             only_local: or_default!(false, $($only_local)?),
 236             type_: $typ,
 237             template: $tpl,
 238             duplicates: $duplicates,
 239             gate: Gated(Stability::Unstable, sym::rustc_attrs, $msg, cfg_fn!(rustc_attrs)),
 240         }
 241     };
 242 }
 243
 244 macro_rules! experimental {
 245     ($attr:ident) => {
 246         concat!("the `#[", stringify!($attr), "]` attribute is an experimental feature")
 247     };
 248 }
 249
 250 const IMPL_DETAIL: &str = "internal implementation detail";
 251 const INTERNAL_UNSTABLE: &str = "this is an internal attribute that will never be stable";
 252
 253 pub struct BuiltinAttribute {
 254     pub name: Symbol,
 255     /// Whether this attribute is only used in the local crate.
 256     ///
 257     /// If so, it is not encoded in the crate metadata.
 258     pub only_local: bool,
 259     pub type_: AttributeType,
 260     pub template: AttributeTemplate,
 261     pub duplicates: AttributeDuplicates,
 262     pub gate: AttributeGate,
 263 }
 264
 265 /// Attributes that have a special meaning to rustc or rustdoc.
 266 #[rustfmt::skip]
 267 pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
 268     // ==========================================================================
 269     // Stable attributes:
 270     // ==========================================================================
 271
 272     // Conditional compilation:
 273     ungated!(cfg, Normal, template!(List: "predicate"), DuplicatesOk),
 274     ungated!(cfg_attr, Normal, template!(List: "predicate, attr1, attr2, ..."), DuplicatesOk),
 275
 276     // Testing:
 277     ungated!(ignore, Normal, template!(Word, NameValueStr: "reason"), WarnFollowing),
 278     ungated!(
 279         should_panic, Normal,
 280         template!(Word, List: r#"expected = "reason"#, NameValueStr: "reason"), FutureWarnFollowing,
 281     ),
 282     // FIXME(Centril): This can be used on stable but shouldn't.
 283     ungated!(reexport_test_harness_main, CrateLevel, template!(NameValueStr: "name"), ErrorFollowing),
 284
 285     // Macros:
 286     ungated!(automatically_derived, Normal, template!(Word), WarnFollowing),
 287     ungated!(macro_use, Normal, template!(Word, List: "name1, name2, ..."), WarnFollowingWordOnly),
 288     ungated!(macro_escape, Normal, template!(Word), WarnFollowing), // Deprecated synonym for `macro_use`.
 289     ungated!(macro_export, Normal, template!(Word, List: "local_inner_macros"), WarnFollowing),
 290     ungated!(proc_macro, Normal, template!(Word), ErrorFollowing),
 291     ungated!(
 292         proc_macro_derive, Normal,
 293         template!(List: "TraitName, /*opt*/ attributes(name1, name2, ...)"), ErrorFollowing,
 294     ),
 295     ungated!(proc_macro_attribute, Normal, template!(Word), ErrorFollowing),
 296
 297     // Lints:
 298     ungated!(
 299         warn, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#), DuplicatesOk
 300     ),
 301     ungated!(
 302         allow, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#), DuplicatesOk
 303     ),
 304     gated!(
 305         expect, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#), DuplicatesOk,
 306         lint_reasons, experimental!(expect)
 307     ),
 308     ungated!(
 309         forbid, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#), DuplicatesOk
 310     ),
 311     ungated!(
 312         deny, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#), DuplicatesOk
 313     ),
 314     ungated!(must_use, Normal, template!(Word, NameValueStr: "reason"), FutureWarnFollowing),
 315     gated!(
 316         must_not_suspend, Normal, template!(Word, NameValueStr: "reason"), WarnFollowing,
 317         experimental!(must_not_suspend)
 318     ),
 319     ungated!(
 320         deprecated, Normal,
 321         template!(
 322             Word,
 323             List: r#"/*opt*/ since = "version", /*opt*/ note = "reason""#,
 324             NameValueStr: "reason"
 325         ),
 326         ErrorFollowing
 327     ),
 328
 329     // Crate properties:
 330     ungated!(crate_name, CrateLevel, template!(NameValueStr: "name"), FutureWarnFollowing),
 331     ungated!(crate_type, CrateLevel, template!(NameValueStr: "bin|lib|..."), DuplicatesOk),
 332     // crate_id is deprecated
 333     ungated!(crate_id, CrateLevel, template!(NameValueStr: "ignored"), FutureWarnFollowing),
 334
 335     // ABI, linking, symbols, and FFI
 336     ungated!(
 337         link, Normal,
 338         template!(List: r#"name = "...", /*opt*/ kind = "dylib|static|...", /*opt*/ wasm_import_module = "...""#),
 339         DuplicatesOk,
 340     ),
 341     ungated!(link_name, Normal, template!(NameValueStr: "name"), FutureWarnPreceding),
 342     ungated!(no_link, Normal, template!(Word), WarnFollowing),
 343     ungated!(repr, Normal, template!(List: "C"), DuplicatesOk),
 344     ungated!(export_name, Normal, template!(NameValueStr: "name"), FutureWarnPreceding),
 345     ungated!(link_section, Normal, template!(NameValueStr: "name"), FutureWarnPreceding),
 346     ungated!(no_mangle, Normal, template!(Word), WarnFollowing, @only_local: true),
 347     ungated!(used, Normal, template!(Word, List: "compiler|linker"), WarnFollowing, @only_local: true),
 348
 349     // Limits:
 350     ungated!(recursion_limit, CrateLevel, template!(NameValueStr: "N"), FutureWarnFollowing),
 351     ungated!(type_length_limit, CrateLevel, template!(NameValueStr: "N"), FutureWarnFollowing),
 352     gated!(
 353         const_eval_limit, CrateLevel, template!(NameValueStr: "N"), ErrorFollowing,
 354         const_eval_limit, experimental!(const_eval_limit)
 355     ),
 356     gated!(
 357         move_size_limit, CrateLevel, template!(NameValueStr: "N"), ErrorFollowing,
 358         large_assignments, experimental!(move_size_limit)
 359     ),
 360
 361     // Entry point:
 362     ungated!(start, Normal, template!(Word), WarnFollowing),
 363     ungated!(no_start, CrateLevel, template!(Word), WarnFollowing),
 364     ungated!(no_main, CrateLevel, template!(Word), WarnFollowing),
 365
 366     // Modules, prelude, and resolution:
 367     ungated!(path, Normal, template!(NameValueStr: "file"), FutureWarnFollowing),
 368     ungated!(no_std, CrateLevel, template!(Word), WarnFollowing),
 369     ungated!(no_implicit_prelude, Normal, template!(Word), WarnFollowing),
 370     ungated!(non_exhaustive, Normal, template!(Word), WarnFollowing),
 371
 372     // Runtime
 373     ungated!(
 374         windows_subsystem, CrateLevel,
 375         template!(NameValueStr: "windows|console"), FutureWarnFollowing
 376     ),
 377     ungated!(panic_handler, Normal, template!(Word), WarnFollowing), // RFC 2070
 378
 379     // Code generation:
 380     ungated!(inline, Normal, template!(Word, List: "always|never"), FutureWarnFollowing, @only_local: true),
 381     ungated!(cold, Normal, template!(Word), WarnFollowing, @only_local: true),
 382     ungated!(no_builtins, CrateLevel, template!(Word), WarnFollowing),
 383     ungated!(target_feature, Normal, template!(List: r#"enable = "name""#), DuplicatesOk),
 384     ungated!(track_caller, Normal, template!(Word), WarnFollowing),
 385     gated!(
 386         no_sanitize, Normal,
 387         template!(List: "address, memory, thread"), DuplicatesOk,
 388         experimental!(no_sanitize)
 389     ),
 390     gated!(no_coverage, Normal, template!(Word), WarnFollowing, experimental!(no_coverage)),
 391
 392     ungated!(
 393         doc, Normal, template!(List: "hidden|inline|...", NameValueStr: "string"), DuplicatesOk
 394     ),
 395
 396     // ==========================================================================
 397     // Unstable attributes:
 398     // ==========================================================================
 399
 400     // RFC #3191: #[debugger_visualizer] support
 401     gated!(
 402         debugger_visualizer, Normal, template!(List: r#"natvis_file = "...""#),
 403         DuplicatesOk, experimental!(debugger_visualizer)
 404     ),
 405
 406     // Linking:
 407     gated!(naked, Normal, template!(Word), WarnFollowing, @only_local: true, naked_functions, experimental!(naked)),
 408     gated!(
 409         link_ordinal, Normal, template!(List: "ordinal"), ErrorPreceding, raw_dylib,
 410         experimental!(link_ordinal)
 411     ),
 412
 413     // Plugins:
 414     BuiltinAttribute {
 415         name: sym::plugin,
 416         only_local: false,
 417         type_: CrateLevel,
 418         template: template!(List: "name"),
 419         duplicates: DuplicatesOk,
 420         gate: Gated(
 421             Stability::Deprecated(
 422                 "https://github.com/rust-lang/rust/pull/64675",
 423                 Some("may be removed in a future compiler version"),
 424             ),
 425             sym::plugin,
 426             "compiler plugins are deprecated",
 427             cfg_fn!(plugin)
 428         ),
 429     },
 430
 431     // Testing:
 432     gated!(
 433         test_runner, CrateLevel, template!(List: "path"), ErrorFollowing, custom_test_frameworks,
 434         "custom test frameworks are an unstable feature",
 435     ),
 436     // RFC #1268
 437     gated!(
 438         marker, Normal, template!(Word), WarnFollowing, marker_trait_attr, experimental!(marker)
 439     ),
 440     gated!(
 441         thread_local, Normal, template!(Word), WarnFollowing,
 442         "`#[thread_local]` is an experimental feature, and does not currently handle destructors",
 443     ),
 444     gated!(no_core, CrateLevel, template!(Word), WarnFollowing, experimental!(no_core)),
 445     // RFC 2412
 446     gated!(
 447         optimize, Normal, template!(List: "size|speed"), ErrorPreceding, optimize_attribute,
 448         experimental!(optimize),
 449     ),
 450     // RFC 2867
 451     gated!(
 452         instruction_set, Normal, template!(List: "set"), ErrorPreceding,
 453         isa_attribute, experimental!(instruction_set)
 454     ),
 455
 456     gated!(
 457         ffi_returns_twice, Normal, template!(Word), WarnFollowing, experimental!(ffi_returns_twice)
 458     ),
 459     gated!(ffi_pure, Normal, template!(Word), WarnFollowing, experimental!(ffi_pure)),
 460     gated!(ffi_const, Normal, template!(Word), WarnFollowing, experimental!(ffi_const)),
 461     gated!(
 462         register_attr, CrateLevel, template!(List: "attr1, attr2, ..."), DuplicatesOk,
 463         experimental!(register_attr),
 464     ),
 465     gated!(
 466         register_tool, CrateLevel, template!(List: "tool1, tool2, ..."), DuplicatesOk,
 467         experimental!(register_tool),
 468     ),
 469
 470     gated!(
 471         cmse_nonsecure_entry, Normal, template!(Word), WarnFollowing,
 472         experimental!(cmse_nonsecure_entry)
 473     ),
 474     // RFC 2632
 475     gated!(
 476         default_method_body_is_const, Normal, template!(Word), WarnFollowing, const_trait_impl,
 477         "`default_method_body_is_const` is a temporary placeholder for declaring default bodies \
 478         as `const`, which may be removed or renamed in the future."
 479     ),
 480     // lang-team MCP 147
 481     gated!(
 482         deprecated_safe, Normal, template!(List: r#"since = "version", note = "...""#), ErrorFollowing,
 483         experimental!(deprecated_safe),
 484     ),
 485
 486     // ==========================================================================
 487     // Internal attributes: Stability, deprecation, and unsafe:
 488     // ==========================================================================
 489
 490     ungated!(feature, CrateLevel, template!(List: "name1, name2, ..."), DuplicatesOk),
 491     // FIXME(jhpratt) remove this eventually
 492     ungated!(
 493         rustc_deprecated, Normal,
 494         template!(List: r#"since = "version", note = "...""#), ErrorFollowing
 495     ),
 496     // DuplicatesOk since it has its own validation
 497     ungated!(
 498         stable, Normal, template!(List: r#"feature = "name", since = "version""#), DuplicatesOk,
 499     ),
 500     ungated!(
 501         unstable, Normal,
 502         template!(List: r#"feature = "name", reason = "...", issue = "N""#), DuplicatesOk,
 503     ),
 504     ungated!(rustc_const_unstable, Normal, template!(List: r#"feature = "name""#), DuplicatesOk),
 505     ungated!(rustc_const_stable, Normal, template!(List: r#"feature = "name""#), DuplicatesOk),
 506     gated!(
 507         allow_internal_unstable, Normal, template!(Word, List: "feat1, feat2, ..."), DuplicatesOk,
 508         "allow_internal_unstable side-steps feature gating and stability checks",
 509     ),
 510     gated!(
 511         rustc_allow_const_fn_unstable, Normal,
 512         template!(Word, List: "feat1, feat2, ..."), DuplicatesOk,
 513         "rustc_allow_const_fn_unstable side-steps feature gating and stability checks"
 514     ),
 515     gated!(
 516         allow_internal_unsafe, Normal, template!(Word), WarnFollowing,
 517         "allow_internal_unsafe side-steps the unsafe_code lint",
 518     ),
 519
 520     // ==========================================================================
 521     // Internal attributes: Type system related:
 522     // ==========================================================================
 523
 524     gated!(fundamental, Normal, template!(Word), WarnFollowing, experimental!(fundamental)),
 525     gated!(
 526         may_dangle, Normal, template!(Word), WarnFollowing, dropck_eyepatch,
 527         "`may_dangle` has unstable semantics and may be removed in the future",
 528     ),
 529
 530     // ==========================================================================
 531     // Internal attributes: Runtime related:
 532     // ==========================================================================
 533
 534     rustc_attr!(rustc_allocator, Normal, template!(Word), WarnFollowing, IMPL_DETAIL),
 535     rustc_attr!(rustc_allocator_nounwind, Normal, template!(Word), WarnFollowing, IMPL_DETAIL),
 536     gated!(
 537         alloc_error_handler, Normal, template!(Word), WarnFollowing,
 538         experimental!(alloc_error_handler)
 539     ),
 540     gated!(
 541         default_lib_allocator, Normal, template!(Word), WarnFollowing, allocator_internals,
 542         experimental!(default_lib_allocator),
 543     ),
 544     gated!(
 545         needs_allocator, Normal, template!(Word), WarnFollowing, allocator_internals,
 546         experimental!(needs_allocator),
 547     ),
 548     gated!(panic_runtime, Normal, template!(Word), WarnFollowing, experimental!(panic_runtime)),
 549     gated!(
 550         needs_panic_runtime, Normal, template!(Word), WarnFollowing,
 551         experimental!(needs_panic_runtime)
 552     ),
 553     gated!(
 554         compiler_builtins, Normal, template!(Word), WarnFollowing,
 555         "the `#[compiler_builtins]` attribute is used to identify the `compiler_builtins` crate \
 556         which contains compiler-rt intrinsics and will never be stable",
 557     ),
 558     gated!(
 559         profiler_runtime, Normal, template!(Word), WarnFollowing,
 560         "the `#[profiler_runtime]` attribute is used to identify the `profiler_builtins` crate \
 561         which contains the profiler runtime and will never be stable",
 562     ),
 563
 564     // ==========================================================================
 565     // Internal attributes, Linkage:
 566     // ==========================================================================
 567
 568     gated!(
 569         linkage, Normal, template!(NameValueStr: "external|internal|..."), ErrorPreceding, @only_local: true,
 570         "the `linkage` attribute is experimental and not portable across platforms",
 571     ),
 572     rustc_attr!(
 573         rustc_std_internal_symbol, Normal, template!(Word), WarnFollowing, @only_local: true, INTERNAL_UNSTABLE
 574     ),
 575
 576     // ==========================================================================
 577     // Internal attributes, Macro related:
 578     // ==========================================================================
 579
 580     rustc_attr!(
 581         rustc_builtin_macro, Normal,
 582         template!(Word, List: "name, /*opt*/ attributes(name1, name2, ...)"), ErrorFollowing,
 583         IMPL_DETAIL,
 584     ),
 585     rustc_attr!(rustc_proc_macro_decls, Normal, template!(Word), WarnFollowing, INTERNAL_UNSTABLE),
 586     rustc_attr!(
 587         rustc_macro_transparency, Normal,
 588         template!(NameValueStr: "transparent|semitransparent|opaque"), ErrorFollowing,
 589         "used internally for testing macro hygiene",
 590     ),
 591
 592     // ==========================================================================
 593     // Internal attributes, Diagnostics related:
 594     // ==========================================================================
 595
 596     rustc_attr!(
 597         rustc_on_unimplemented, Normal,
 598         template!(
 599             List: r#"/*opt*/ message = "...", /*opt*/ label = "...", /*opt*/ note = "...""#,
 600             NameValueStr: "message"
 601         ),
 602         ErrorFollowing,
 603         INTERNAL_UNSTABLE
 604     ),
 605     // Enumerates "identity-like" conversion methods to suggest on type mismatch.
 606     rustc_attr!(
 607         rustc_conversion_suggestion, Normal, template!(Word), WarnFollowing, INTERNAL_UNSTABLE
 608     ),
 609     // Prevents field reads in the marked trait or method to be considered
 610     // during dead code analysis.
 611     rustc_attr!(
 612         rustc_trivial_field_reads, Normal, template!(Word), WarnFollowing, INTERNAL_UNSTABLE
 613     ),
 614     // Used by the `rustc::potential_query_instability` lint to warn methods which
 615     // might not be stable during incremental compilation.
 616     rustc_attr!(rustc_lint_query_instability, Normal, template!(Word), WarnFollowing, INTERNAL_UNSTABLE),
 617
 618     // ==========================================================================
 619     // Internal attributes, Const related:
 620     // ==========================================================================
 621
 622     rustc_attr!(rustc_promotable, Normal, template!(Word), WarnFollowing, IMPL_DETAIL),
 623     rustc_attr!(
 624         rustc_legacy_const_generics, Normal, template!(List: "N"), ErrorFollowing,
 625         INTERNAL_UNSTABLE
 626     ),
 627     // Do not const-check this function's body. It will always get replaced during CTFE.
 628     rustc_attr!(
 629         rustc_do_not_const_check, Normal, template!(Word), WarnFollowing, INTERNAL_UNSTABLE
 630     ),
 631
 632     // ==========================================================================
 633     // Internal attributes, Layout related:
 634     // ==========================================================================
 635
 636     rustc_attr!(
 637         rustc_layout_scalar_valid_range_start, Normal, template!(List: "value"), ErrorFollowing,
 638         "the `#[rustc_layout_scalar_valid_range_start]` attribute is just used to enable \
 639         niche optimizations in libcore and libstd and will never be stable",
 640     ),
 641     rustc_attr!(
 642         rustc_layout_scalar_valid_range_end, Normal, template!(List: "value"), ErrorFollowing,
 643         "the `#[rustc_layout_scalar_valid_range_end]` attribute is just used to enable \
 644         niche optimizations in libcore and libstd and will never be stable",
 645     ),
 646     rustc_attr!(
 647         rustc_nonnull_optimization_guaranteed, Normal, template!(Word), WarnFollowing,
 648         "the `#[rustc_nonnull_optimization_guaranteed]` attribute is just used to enable \
 649         niche optimizations in libcore and libstd and will never be stable",
 650     ),
 651
 652     // ==========================================================================
 653     // Internal attributes, Misc:
 654     // ==========================================================================
 655     gated!(
 656         lang, Normal, template!(NameValueStr: "name"), DuplicatesOk, @only_local: true, lang_items,
 657         "language items are subject to change",
 658     ),
 659     rustc_attr!(
 660         rustc_pass_by_value, Normal,
 661         template!(Word), ErrorFollowing,
 662         "#[rustc_pass_by_value] is used to mark types that must be passed by value instead of reference."
 663     ),
 664     rustc_attr!(
 665         rustc_coherence_is_core, AttributeType::CrateLevel, template!(Word), ErrorFollowing, @only_local: true,
 666         "#![rustc_coherence_is_core] allows inherent methods on builtin types, only intended to be used in `core`."
 667     ),
 668     rustc_attr!(
 669         rustc_allow_incoherent_impl, AttributeType::Normal, template!(Word), ErrorFollowing, @only_local: true,
 670         "#[rustc_allow_incoherent_impl] has to be added to all impl items of an incoherent inherent impl."
 671     ),
 672     rustc_attr!(
 673         rustc_has_incoherent_inherent_impls, AttributeType::Normal, template!(Word), ErrorFollowing,
 674         "#[rustc_has_incoherent_inherent_impls] allows the addition of incoherent inherent impls for \
 675          the given type by annotating all impl items with #[rustc_allow_incoherent_impl]."
 676     ),
 677     BuiltinAttribute {
 678         name: sym::rustc_diagnostic_item,
 679         // FIXME: This can be `true` once we always use `tcx.is_diagnostic_item`.
 680         only_local: false,
 681         type_: Normal,
 682         template: template!(NameValueStr: "name"),
 683         duplicates: ErrorFollowing,
 684         gate: Gated(
 685             Stability::Unstable,
 686             sym::rustc_attrs,
 687             "diagnostic items compiler internal support for linting",
 688             cfg_fn!(rustc_attrs),
 689         ),
 690     },
 691     gated!(
 692         // Used in resolve:
 693         prelude_import, Normal, template!(Word), WarnFollowing,
 694         "`#[prelude_import]` is for use by rustc only",
 695     ),
 696     gated!(
 697         rustc_paren_sugar, Normal, template!(Word), WarnFollowing, unboxed_closures,
 698         "unboxed_closures are still evolving",
 699     ),
 700     rustc_attr!(
 701         rustc_inherit_overflow_checks, Normal, template!(Word), WarnFollowing, @only_local: true,
 702         "the `#[rustc_inherit_overflow_checks]` attribute is just used to control \
 703         overflow checking behavior of several libcore functions that are inlined \
 704         across crates and will never be stable",
 705     ),
 706     rustc_attr!(
 707         rustc_reservation_impl, Normal,
 708         template!(NameValueStr: "reservation message"), ErrorFollowing,
 709         "the `#[rustc_reservation_impl]` attribute is internally used \
 710          for reserving for `for<T> From<!> for T` impl"
 711     ),
 712     rustc_attr!(
 713         rustc_test_marker, Normal, template!(Word), WarnFollowing,
 714         "the `#[rustc_test_marker]` attribute is used internally to track tests",
 715     ),
 716     rustc_attr!(
 717         rustc_unsafe_specialization_marker, Normal, template!(Word), WarnFollowing,
 718         "the `#[rustc_unsafe_specialization_marker]` attribute is used to check specializations"
 719     ),
 720     rustc_attr!(
 721         rustc_specialization_trait, Normal, template!(Word), WarnFollowing,
 722         "the `#[rustc_specialization_trait]` attribute is used to check specializations"
 723     ),
 724     rustc_attr!(
 725         rustc_main, Normal, template!(Word), WarnFollowing,
 726         "the `#[rustc_main]` attribute is used internally to specify test entry point function",
 727     ),
 728     rustc_attr!(
 729         rustc_skip_array_during_method_dispatch, Normal, template!(Word), WarnFollowing,
 730         "the `#[rustc_skip_array_during_method_dispatch]` attribute is used to exclude a trait \
 731         from method dispatch when the receiver is an array, for compatibility in editions < 2021."
 732     ),
 733     rustc_attr!(
 734         rustc_must_implement_one_of, Normal, template!(List: "function1, function2, ..."), ErrorFollowing,
 735         "the `#[rustc_must_implement_one_of]` attribute is used to change minimal complete \
 736         definition of a trait, it's currently in experimental form and should be changed before \
 737         being exposed outside of the std"
 738     ),
 739
 740     // ==========================================================================
 741     // Internal attributes, Testing:
 742     // ==========================================================================
 743
 744     rustc_attr!(TEST, rustc_outlives, Normal, template!(Word), WarnFollowing),
 745     rustc_attr!(TEST, rustc_capture_analysis, Normal, template!(Word), WarnFollowing),
 746     rustc_attr!(TEST, rustc_insignificant_dtor, Normal, template!(Word), WarnFollowing),
 747     rustc_attr!(TEST, rustc_strict_coherence, Normal, template!(Word), WarnFollowing),
 748     rustc_attr!(TEST, rustc_variance, Normal, template!(Word), WarnFollowing),
 749     rustc_attr!(TEST, rustc_layout, Normal, template!(List: "field1, field2, ..."), WarnFollowing),
 750     rustc_attr!(TEST, rustc_regions, Normal, template!(Word), WarnFollowing),
 751     rustc_attr!(
 752         TEST, rustc_error, Normal,
 753         template!(Word, List: "delay_span_bug_from_inside_query"), WarnFollowingWordOnly
 754     ),
 755     rustc_attr!(TEST, rustc_dump_user_substs, Normal, template!(Word), WarnFollowing),
 756     rustc_attr!(TEST, rustc_evaluate_where_clauses, Normal, template!(Word), WarnFollowing),
 757     rustc_attr!(
 758         TEST, rustc_if_this_changed, Normal, template!(Word, List: "DepNode"), DuplicatesOk
 759     ),
 760     rustc_attr!(
 761         TEST, rustc_then_this_would_need, Normal, template!(List: "DepNode"), DuplicatesOk
 762     ),
 763     rustc_attr!(
 764         TEST, rustc_clean, Normal,
 765         template!(List: r#"cfg = "...", /*opt*/ label = "...", /*opt*/ except = "...""#),
 766         DuplicatesOk,
 767     ),
 768     rustc_attr!(
 769         TEST, rustc_partition_reused, Normal,
 770         template!(List: r#"cfg = "...", module = "...""#), DuplicatesOk,
 771     ),
 772     rustc_attr!(
 773         TEST, rustc_partition_codegened, Normal,
 774         template!(List: r#"cfg = "...", module = "...""#), DuplicatesOk,
 775     ),
 776     rustc_attr!(
 777         TEST, rustc_expected_cgu_reuse, Normal,
 778         template!(List: r#"cfg = "...", module = "...", kind = "...""#), DuplicatesOk,
 779     ),
 780     rustc_attr!(TEST, rustc_symbol_name, Normal, template!(Word), WarnFollowing),
 781     rustc_attr!(TEST, rustc_polymorphize_error, Normal, template!(Word), WarnFollowing),
 782     rustc_attr!(TEST, rustc_def_path, Normal, template!(Word), WarnFollowing),
 783     rustc_attr!(TEST, rustc_mir, Normal, template!(List: "arg1, arg2, ..."), DuplicatesOk),
 784     rustc_attr!(TEST, rustc_dump_program_clauses, Normal, template!(Word), WarnFollowing),
 785     rustc_attr!(TEST, rustc_dump_env_program_clauses, Normal, template!(Word), WarnFollowing),
 786     rustc_attr!(TEST, rustc_object_lifetime_default, Normal, template!(Word), WarnFollowing),
 787     rustc_attr!(TEST, rustc_dump_vtable, Normal, template!(Word), WarnFollowing),
 788     rustc_attr!(TEST, rustc_dummy, Normal, template!(Word /* doesn't matter*/), DuplicatesOk),
 789     gated!(
 790         omit_gdb_pretty_printer_section, Normal, template!(Word), WarnFollowing,
 791         "the `#[omit_gdb_pretty_printer_section]` attribute is just used for the Rust test suite",
 792     ),
 793 ];
 794
 795 pub fn deprecated_attributes() -> Vec<&'static BuiltinAttribute> {
 796     BUILTIN_ATTRIBUTES.iter().filter(|attr| attr.gate.is_deprecated()).collect()
 797 }
 798
 799 pub fn is_builtin_attr_name(name: Symbol) -> bool {
 800     BUILTIN_ATTRIBUTE_MAP.get(&name).is_some()
 801 }
 802
 803 pub fn is_builtin_only_local(name: Symbol) -> bool {
 804     BUILTIN_ATTRIBUTE_MAP.get(&name).map_or(false, |attr| attr.only_local)
 805 }
 806
 807 pub static BUILTIN_ATTRIBUTE_MAP: SyncLazy<FxHashMap<Symbol, &BuiltinAttribute>> =
 808     SyncLazy::new(|| {
 809         let mut map = FxHashMap::default();
 810         for attr in BUILTIN_ATTRIBUTES.iter() {
 811             if map.insert(attr.name, attr).is_some() {
 812                 panic!("duplicate builtin attribute `{}`", attr.name);
 813             }
 814         }
 815         map
 816     });